1. Field of the Invention
The present invention relates to printers provided with thermal heads having a reduced dimension in a direction perpendicular to the arrayed direction of heater elements.
2. Description of the Related Art
In a typical thermal printer, a thermal head defining a recording head is provided with a substrate on which a plurality of heater elements formed of an exothermic resistor is arrayed. Based on recording data, electricity is selectively supplied to the heater elements to generate heat in the selected heater elements so that a desired recording operation can be performed on various types of recording media. For example, the heated heater elements melt the ink contained in an ink ribbon in order to heat-transfer the ink to, for example, a sheet of plain paper or a transparency sheet, or develop colors on a sheet of thermal recording paper.
In such a conventional thermal head, an insulating layer is disposed on the surface of the exothermic substrate. An end portion of the top surface of the insulating layer is provided with a projection having a predetermined height. Moreover, an exothermic resistor is disposed over the projection of the insulating layer. The side of the exothermic resistor closer to the front end of the substrate and the side closer to the base end are respectively provided with a common electrode and independent electrodes for supplying power to the exothermic resistor. The region of the exothermic resistor between the common electrode and the independent electrodes defines a plurality of heater elements arrayed across the region in a dot-like manner.
Moreover, the base end portion of the substrate is provided with a driver-IC chip connected with the common electrode and the independent electrodes. The driver-IC chip will be referred to as an IC chip hereinafter. The IC chip is coated with a protective sealing member composed of sealing resin.
Such a conventional thermal head is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2003-165240. According to such a thermal head, the substrate is attached to a printer via a head attachment-base in a manner such that when the head attachment-base is rotated, the heater elements become in contact with and pressed against a platen via a medium.
Like other electric devices, it is in great demand that the size and the cost be reduced in printers provided with the thermal head described above. Such size reduction of printers can be achieved by dramatically reducing the dimension of the substrate of the thermal head in a direction perpendicular to the arrayed direction of the heater elements. Furthermore, by increasing the number of substrates used for thermal heads that are cut and obtained from a single sheet of a mother substrate, the cost reduction can be achieved.
If the dimension of the substrate in the direction perpendicular to the arrayed direction of the heater elements is reduced, the sealing member for coating the IC chip has to be disposed very close to the heater elements on the top surface of the substrate. This means that the sealing member disposed on the thermal head will be positioned in a conveying path of media used for the recording operation, such as paper and ink ribbon. Thus, by coming into contact with the media, the sealing member can interfere with the conveying path, which may lead to improper conveying of the media. Moreover, a direct contact between the sealing member and the media can cause degradation of the recording quality. Furthermore, if the sealing member comes into contact with the platen, the heater elements are prevented from properly pressing against the media. In such a case, high quality recording cannot be achieved.